1. Field of the Invention
This invention relates to tape storage systems and, more specifically, to such systems which are suitable for rack mounting.
2. General Background and State of the Art
Tape libraries are known in the field as indicated by U.S. Pat. No. 5,498,116, granted Mar. 12, 1996, and as disclosed in U.S. patent application Ser. No. 08/427,884, filed Apr. 26, 1995, now U.S. Pat. No. 6,271,982, and assigned to the assignee of this invention. In these systems, a large number of tape cassettes or cartridges are stored in tower-like configurations, and transfer mechanisms are provided for selecting designated tape cassettes and transporting them to a tape drive where data may be accessed from the tape cassettes or written into the tape cassette or cartridge.
One disadvantage of these known prior art arrangements is that they take up more space than is desirable. Thus, for example, standard electronic racks for mounting electronic equipment are normally 19 inches wide and have vertical spaces for storing electronic equipment in, in terms of standard increments or units of height equal to one and three quarters (1xc2xe) inches. Electronic equipment intended for rack mounting is normally designed to occupy a predetermined number of units of height, such as one unit of height (1xc2xe inches) or two or three units of height (3xc2xd inches or 5xc2xc inches, respectively).
If the prior art tape library systems as identified above were to be mounted in standard electronic racks, they would occupy a large number of rack units of height, and this would be considered very wasteful of available rack space.
Another factor to be considered is that prior art tape library systems are often designed to accommodate only one type of cassette, for example an 8 mm tape cassette or one of the xc2xd-inch wide tape cassettes; and each system must be uniquely designed to handle the specific type of cassette.
Accordingly, one object of the invention is to provide a more compact tape library system which will accommodate a large number of cassettes, and only occupy a few rack units of space.
Another object of the invention is to provide a tape library design in which there is a high degree of commonality in the parts which are included in systems for handling different types of tape cassettes.
In accordance with one illustrative embodiment of the invention, the foregoing objects are achieved in a tape library system which includes an array of rectangular platforms, with the platforms being mounted adjacent one another for movement in a plane. Cassette magazines are mounted on the platforms. A cassette handling station is provided immediately adjacent the platforms, and a mechanism is provided for shifting the position of the platforms to bring selected magazines to the cassette handling station. Each system is provided with one or more tape drives, and a transfer carriage for gripping a selected cassette and transferring it to the drive or drives.
In a preferred embodiment, a track is provided and each of the platforms has a depending guide for riding in the track and a cam follower for engagement by a plurality of cams underlying the track.
In a preferred embodiment, the number of platforms is one less than the number of platform stations for maximum cassette density. Four cams may be provided with two at each end of the system with axes of rotation of the cams at each end being displaced from each other. The shifting if platforms is a four-step process, with one cam acting on a single platform at each point in the cycle to apply force to one platform to move that platform (and any aligned platforms) toward the vacant station. Each cam has an extent of 90 degrees and may be operated in a forward or reverse direction to move the magazines in one direction or the other. The reversible capability reduces cassette access time, as the system can act in either direction to bring the selected cassette to the cassette handling station through the shortest path.
In considering the system from an overall standpoint, it may be noted that the vacant station xe2x80x9cmovesxe2x80x9d in the opposite direction from the direction of rotation of the cams and the platforms.
This preferred system as described above has the advantages of both (1) high density because only one station is vacant or open, and (2) reversibility for rapid cassette access.
By substituting different magazines mounted on said platforms, different types of cassettes may be accommodated, while still using the same platform, track and camming arrangements for systems handling different types of cassettes.
In accordance with additional features of the system (1) a number of platform locations may be provided with the number of platforms being one less than the number of platform locations; and (2) the cassette magazines may be facing the cassette handling station as the platforms are shifted in position; (3) the tape drives may be positioned so that the cassettes may be transferred linearly without changing orientation of the cassettes; and (4) with modified optimum platform sizes for each type of cassette, significant commonality of parts and design features may be present in the different systems.
It is also noted in passing that the platforms and platform locations do not have to be immediately adjacent one another, but could be in an open-center rectangular configuration, for example. With arrangements of this type, additional system equipment such as the drive motor and electronics may be located in the open center of the platforms.
Concerning commercially available tape libraries, in the xc2xd-inch tape drive category, one commercially available library system with two drives includes 18 tape cassettes in a five rack-unit space. This compares with the design in accordance with the invention which would include 21 cassettes and two drives in a five rack-unit space. This is an increase in system capacity of about 16%.
In the 8 mm tape drive field, there is one commercially available five rack-unit system which only has 30 cassettes, and the comparable system made in accordance with the invention has a 65 cassette capacity. This design would include 13 platforms with five cassettes in each magazine on each platform. This would involve an increased system capacity of substantially more than 100%.
Other objects, features and advantages of the invention will become apparent from a consideration of the following detailed description and the accompanying drawings.